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1190                          Appendix VL

The circulation of jacket-cooling water is indicated in Fig 1049,
the hot water being pumped from the cylinders to the cooling
radiator, then to the rear tank, returning to the cylinder to once
more absorb heat.     The honeycomb radiator E, Fig. 1048, is
almost universally employed, where brass tubes c c of circular
section are expanded into hexagons at their ends, and are soldered
together by dipping the whole radiator, front and back, to a depth
of J" in a bath of molten tin.   The space D between the tubes is
only a millimetre wide, and thus divides the water stream most
thoroughly when presenting it to the cooling air passed through
the tubes by a fan (Fig. 1041).   The cup A is for filling purposes.
Fly-wheel clutches are   of  two kinds.     The leather-faced
clutch A, Fig. 1050, has an internal spring to keep the inner and
outer cones B and A in contact except when relieved by the foot
lever.   The leather is   kept   greased,  and   must be renewed
annually.   The objection to leather has introduced m|tal-to-metal
clutches, of which the Crossley clutch, Fig. 1050, is an example.
The inner portion consists of a pair of shoes F, hinged above to a
central bracket, which is carried qn a hollow shaft engaging with
the claw clutch on first gear wheel.    Two toggle levers E, con-
nected at their lower ends to the shoes, are united at their upper
ends by a strong spring which presses the shoes outwards against
the fly-wheel.    To release the grip, a foot lever slides the cone c
leftwards, which, pressing on the rollers D, separates the levers at
their upper extremities and draws the shoes together.   The clutch
* 'If '                    surfaces are cylinders, not cones, and they must be kept well

oiled to ensure slipping when required.

After the fly-wheel comes the gear box, Fig. 1051, an im-
portant but unfortunate necessity with all petrol engines. These
are designed for four speeds on large and three speeds on smaller
cars, a reversal being provided in both cases; but any number of
speeds can be easily arranged by an extra pair of wheels for each.
The engine and propeller shaft are disconnected at y, and only
coupled, as required, by clutching wheels A and F together. The
wheel A runs solid with the fly-wheel through a hollow shaft and
flexible coupling, and gears constantly with wheel B on a second-
motion shaft of square section, the rotation being transferred to
the propeller shaft (also of square section) by pairs of wheels, c, D